1. Field of the Invention
The present invention relates to a socket for use in combination with a plug to form a pipe coupling with lock balls and, more particularly, it is related to the structure of a socket which is used for the pipe coupling to connect a small-sized gas cylinder to the piping.
2. Description of the Related Art
Conventionally, the carbon dioxide gas cylinder housed in the automatic vending machine for carbonated drinks was connected to the piping in the automatic vending machine, using a union nut for the base of the gas cylinder.
The space in the automatic vending machine is quite small. Therefore, this connecting manner is excellent is that it needs no large space. When the used gas cylinder was to be exchanged with a new one, however, tools such as the wrench never failed to be needed to thereby make the exchanging operation troublesome.